Since you know a dealer is not doing this out of the goodness of his heart; he is doing it because he thinks he can make money in the deal. Also a dealer is not going to waste his lot space and a salesman’s time and effort for just a few bucks. If he is the high volume dealer,he knows how to price it to sell and make his profit.
Find out what the dealer's best offer is for a flat out purchase of your trailer. If you do not like the deal, you can continue to take the time and effort sell it yourself. The only drawback is, if you do not sell it for the price you want this year, you are stuck with another year’s depreciation.
Be sure to get everything in writing so you know what is what and do not have to depend on memory.